In 1987, the concept of a PhC was respectively proposed by E. Yablonovitch in American Bell Labs when studying how to suppress spontaneous radiation and S. John in Princeton University when studying photon localization. The PhC has a material structure of a dielectric material arranged periodically in space, and is often an artificial crystal formed by two or more than two materials having different dielectric constants.
Control on light is one of main challenges in modern optics. With increasing development of optical communication and computer technology, it becomes more important to control and operate light signals. Since the PhC has the property of allowing light at a specific frequency and a specific direction to pass or forbidding in the PhC, the researches on the PhC have received people's attention.
Because the electromagnetic field mode in an absolute PBG is completely nonexistent, when an electron energy band is superposed with the absolute PBGs of the PhC, the spontaneous radiation is suppressed. The absolute PBGs can change the interaction between a field and a material by controlling the spontaneous radiation and improve the performance of an optical device. The PhC can be applied to semiconductor lasers, solar cells, high-quality resonant cavities and filters.
The distribution of a dielectric material in unit cells of the PhC has a strong impact on the PBGs, the selection of a PBGs has a great impact on the application of the PhC, and particularly, a large absolute PBGs is very effective on the control of broadband signals.
For the light having the frequency in an absolute PBG, it cannot pass any matter for different polarizations and wave vectors. The large PBGs can be used for manufacturing optical waveguides, liquid crystal PhC fibers, negative refractive index imagers, PhC lasers of a defect mode in defect cavities. Large absolute PBGs can suppress spontaneous radiation in PhC lasers of a defect mode, particularly under the condition that the spectral range of spontaneous radiation is very wide. If we desire to obtain PhC resonant cavities with narrow resonant peaks, large absolute PBGs are necessary. In various optical devices, polarization-independent absolute PBGs are very important. Just because many devices of PhCs utilize PBGs, worldwide scientists are striving to design PhC structures with larger absolute PBGs.